The present invention relates to a semiconductor light-emitting device in which light is emitted from an active layer formed between a pair of semiconductor layers, a semiconductor light-emitting apparatus using the semiconductor light-emitting device, and a method of manufacturing the semiconductor light-emitting device. In particular, the invention relates to a semiconductor light-emitting device enhanced in light extraction efficiency, a semiconductor light-emitting apparatus using the semiconductor light-emitting device, and a method of manufacturing the semiconductor light-emitting device.
In the light emitting diode, which is an example of semiconductor light-emitting devices, devices with a structure in which a nitride-based compound semiconductor material represented by a GaN-based semiconductor layer is used have been widely researched and developed. In the light-emitting devices using such a nitride-based compound semiconductor layer, a laminate structure having a p-type layer and an n-type layer with an active layer therebetween is adopted, and it may be necessary that a p-side electrode and an n-side electrode are put in ohmic contact with each of the p-type layer and the n-type layer so as to supply a current injected into the active layer. In this case, for realizing a light-emitting device with a high performance such as a high luminance, it may be indispensable to put the p-side electrode and the n-side electrode into ohmic contact with low resistance.
Meanwhile, the light taken out by injecting a current into the active layer is radiated not only to the face side of the device but also to the back side and the lateral sides of the device. In view of this, there has been known a technology in which a high-reflection film, for example, is formed on the back side of the light-emitting device where the light radiated from the device is unnecessary, whereby the light is reflected on the surface of the high-reflection film, and the light take-out efficiency on the face side or the like can be enhanced accordingly.
Such a high-reflection film is formed of such material as silver and aluminum. For instance, in the case where the ohmic contact is contrived on the side of the p-side electrode as above-mentioned and the like cases, a thin film of a metal capable of realizing the ohmic contact such as Ni, Pt, Mg, Zn, Be, Ag, Au and Ge is formed, before forming the high-reflection film of silver, aluminum or the like.
The metallic material constituting the high-reflection film is excellent in the light-reflecting characteristics, but, in the case of using such a metallic material as an electrode to be used by passing a current therethrough, migration as a diffusion phenomenon arising from heat or the like would be generated, whereby the function as the light-emitting device would be lost in a comparatively short time. Therefore, in the case of enhancing the light take-out efficiency by utilizing a high-reflection film, there is simultaneously a need for a means of restraining the generation of migration.
For enhancing the light take-out efficiency by utilizing such a high-reflection film so as to take out light on the substrate side through light reflection by the high-reflection film and for simultaneously preventing the generation of migration, there has been known a technology in which a barrier film is formed between a film for contriving ohmic contact and the high-reflection metal film. For example, as disclosed in Japanese Patent Laid-out No. 2002-26392, there has been known a technology in which an active layer and a p-type GaN layer are formed on an n-type GaN layer on a substrate, and a thin Ni film, a thin Mo film, and a metal film as a high-reflection film are formed to constitute a p-side electrode structure.
In the device structure described in Japanese Patent Laid-open No. 2002-26392, ohmic contact owing to the Ni film is realized and, simultaneously, a barrier function of the Mo film can prevent the migration of constituent atoms of the high-reflection metal film on the Mo film. However, the Mo film formed as a barrier electrode is a very thin film with a thickness of about 1 nm, and there arises the following problem. In the case where such a very thin metal film is formed on the reflection side, it is difficult to form the film evenly in the plane, so that local dispersions in reflectance are generated, leading to a situation where the reflection characteristic of the high-reflection metal film cannot be utilized sufficiently.
The problem of the dispersions of reflectance in the plane can be solved by enlarging the thickness of the metal film formed as the barrier electrode. However, in the case where the thickness of the metal film as the barrier electrode is enlarged, the light radiated from the active layer may fail to reach the high-reflection metal film, and the significance of the existence of the high-reflection metal film would rather be lost.